From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D7264C433E0 for ; Tue, 19 Jan 2021 04:30:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9E511214D8 for ; Tue, 19 Jan 2021 04:30:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730886AbhASE3l (ORCPT ); Mon, 18 Jan 2021 23:29:41 -0500 Received: from mail.kernel.org ([198.145.29.99]:37958 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730874AbhASE2C (ORCPT ); Mon, 18 Jan 2021 23:28:02 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 8F449207C4; Tue, 19 Jan 2021 04:27:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1611030441; bh=7NwNR5W4ohdUOths1UUy38NvjQ/TF3RD6yRZmGqw8t8=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=KUjPpNlIUyz6kiuYHOhajAb8MEajNmn6SQTF6IqtL9p+Erz0t/h3Fly88+yR4/rKj 92Y78KuPBVkgW6keKU7hp6EyV1CgCeShod7R4XmvuBc6U6+fo85id8NUPa8jZ6zp7W bY56b2vgEhHXD54M+aQFYWSiZ26q9nvpL6KoYNBzjPtyjgrmSAZgy05B392JBpnsTC Yi76ILvvBd1RvguqX/ldD2wu97bzBEKNBd8XDU2uPH1fNpJONRDLYv/C/YL97SfdBi DnHt3DazNtK44taWqYv5Nry/u5DWBAfW3WEIqoAZWf+yiuqQ0cuzcc/+MsB+lfxgH6 ZOaFNNL3F7PCg== Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 4FA1F352268F; Mon, 18 Jan 2021 20:27:21 -0800 (PST) Date: Mon, 18 Jan 2021 20:27:21 -0800 From: "Paul E. McKenney" To: Feng Tang Cc: Borislav Petkov , kernel test robot , Jonathan Lemon , Tony Luck , LKML , x86@kernel.org, lkp@lists.01.org, lkp@intel.com, ying.huang@intel.com, zhengjun.xing@intel.com Subject: Re: [x86/mce] 7bb39313cd: netperf.Throughput_tps -4.5% regression Message-ID: <20210119042721.GA12664@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20210112142109.GE30747@xsang-OptiPlex-9020> <20210112141438.GF13086@zn.tnic> <20210116035251.GB29609@shbuild999.sh.intel.com> <20210116153413.GP2743@paulmck-ThinkPad-P72> <20210116160921.GA101665@shbuild999.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210116160921.GA101665@shbuild999.sh.intel.com> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jan 17, 2021 at 12:09:21AM +0800, Feng Tang wrote: > On Sat, Jan 16, 2021 at 07:34:26AM -0800, Paul E. McKenney wrote: > > On Sat, Jan 16, 2021 at 11:52:51AM +0800, Feng Tang wrote: > > > Hi Boris, > > > > > > On Tue, Jan 12, 2021 at 03:14:38PM +0100, Borislav Petkov wrote: > > > > On Tue, Jan 12, 2021 at 10:21:09PM +0800, kernel test robot wrote: > > > > > > > > > > Greeting, > > > > > > > > > > FYI, we noticed a -4.5% regression of netperf.Throughput_tps due to commit: > > > > > > > > > > > > > > > commit: 7bb39313cd6239e7eb95198950a02b4ad2a08316 ("x86/mce: Make mce_timed_out() identify holdout CPUs") > > > > > https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git ras/core > > > > > > > > > > > > > > > in testcase: netperf > > > > > on test machine: 192 threads Intel(R) Xeon(R) Platinum 9242 CPU @ 2.30GHz with 192G memory > > > > > with following parameters: > > > > > > > > > > ip: ipv4 > > > > > runtime: 300s > > > > > nr_threads: 16 > > > > > cluster: cs-localhost > > > > > test: TCP_CRR > > > > > cpufreq_governor: performance > > > > > ucode: 0x5003003 > > > > > > > > > > test-description: Netperf is a benchmark that can be use to measure various aspect of networking performance. > > > > > test-url: http://www.netperf.org/netperf/ > > > > > > > > I'm very very sceptical this thing benchmarks #MC exception handler > > > > performance. Because the code this patch adds gets run only during a MCE > > > > exception. > > > > > > > > So unless I'm missing something obvious please check your setup. > > > > > > We've tracked some similar strange kernel performance changes, like > > > another mce related one [1]. For many of them, the root cause is > > > the patch changes the code or data alignment/address of other > > > components, as could be seen from System.map file. > > > > > > We added debug patch trying to force data sections of each .o be > > > aligned (isolating components), and run the test 3 times, and > > > the regression is gone. > > > > > > %stddev %change %stddev > > > \ | \ > > > 263059 -0.2% 262523 netperf.Throughput_total_tps > > > 16441 -0.2% 16407 netperf.Throughput_tps > > > > > > So the -4.5% is likely to be caused by data address change. > > > > > > But still there is something I don't understand, that the patch > > > introduces a new cpumask 'mce_missing_cpus', which is 1024B, and > > > from the System.map, all data following it get a 1024B offset, > > > without changing the cacheline alignment situation. > > > > > > 2 original system map files are attached in case people want > > > to check. > > > > > > [1]. https://lore.kernel.org/lkml/20200425114414.GU26573@shao2-debian/ > > > > One possibility is that the data-address changes put more stress on the > > TLB, for example, if that region of memory is not covered by a huge > > TLB entry. If this is the case, is there a convenient way to define > > mce_missing_cpus so as to get it out of the way? > > Yes! I also tried some experiment for dTLB, by adding 3 more cpumask_t > right after 'mce_missing_cpus', so that the total offset will be 4KB. > I expected the regression could be gone, but it turns out to have > a +2.4% improvement. > > 16741 -4.5% 15980 +2.4% 17149 netperf.Throughput_tps > > Which is still kind of out of our control :) I bet that the results vary depending on the type of CPU, and also on the kernel address-space layout, which of course also varies based on the Kconfig options. Let's see how the maintainers would like to proceed. Thanx, Paul From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: multipart/mixed; boundary="===============0916882215342503839==" MIME-Version: 1.0 From: Paul E. McKenney To: lkp@lists.01.org Subject: Re: [x86/mce] 7bb39313cd: netperf.Throughput_tps -4.5% regression Date: Mon, 18 Jan 2021 20:27:21 -0800 Message-ID: <20210119042721.GA12664@paulmck-ThinkPad-P72> In-Reply-To: <20210116160921.GA101665@shbuild999.sh.intel.com> List-Id: --===============0916882215342503839== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable On Sun, Jan 17, 2021 at 12:09:21AM +0800, Feng Tang wrote: > On Sat, Jan 16, 2021 at 07:34:26AM -0800, Paul E. McKenney wrote: > > On Sat, Jan 16, 2021 at 11:52:51AM +0800, Feng Tang wrote: > > > Hi Boris, > > > = > > > On Tue, Jan 12, 2021 at 03:14:38PM +0100, Borislav Petkov wrote: > > > > On Tue, Jan 12, 2021 at 10:21:09PM +0800, kernel test robot wrote: > > > > > = > > > > > Greeting, > > > > > = > > > > > FYI, we noticed a -4.5% regression of netperf.Throughput_tps due = to commit: > > > > > = > > > > > = > > > > > commit: 7bb39313cd6239e7eb95198950a02b4ad2a08316 ("x86/mce: Make = mce_timed_out() identify holdout CPUs") > > > > > https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git ras/core > > > > > = > > > > > = > > > > > in testcase: netperf > > > > > on test machine: 192 threads Intel(R) Xeon(R) Platinum 9242 CPU @= 2.30GHz with 192G memory > > > > > with following parameters: > > > > > = > > > > > ip: ipv4 > > > > > runtime: 300s > > > > > nr_threads: 16 > > > > > cluster: cs-localhost > > > > > test: TCP_CRR > > > > > cpufreq_governor: performance > > > > > ucode: 0x5003003 > > > > > = > > > > > test-description: Netperf is a benchmark that can be use to measu= re various aspect of networking performance. > > > > > test-url: http://www.netperf.org/netperf/ > > > > = > > > > I'm very very sceptical this thing benchmarks #MC exception handler > > > > performance. Because the code this patch adds gets run only during = a MCE > > > > exception. > > > > = > > > > So unless I'm missing something obvious please check your setup. > > > = > > > We've tracked some similar strange kernel performance changes, like > > > another mce related one [1]. For many of them, the root cause is > > > the patch changes the code or data alignment/address of other > > > components, as could be seen from System.map file. > > > = > > > We added debug patch trying to force data sections of each .o be > > > aligned (isolating components), and run the test 3 times, and > > > the regression is gone. > > > = > > > %stddev %change %stddev > > > \ | \ = > > > 263059 -0.2% 262523 netperf.Throughput_tota= l_tps > > > 16441 -0.2% 16407 netperf.Throughput_tps > > > = > > > So the -4.5% is likely to be caused by data address change. = > > > = > > > But still there is something I don't understand, that the patch > > > introduces a new cpumask 'mce_missing_cpus', which is 1024B, and > > > from the System.map, all data following it get a 1024B offset, > > > without changing the cacheline alignment situation. > > > = > > > 2 original system map files are attached in case people want > > > to check. > > > = > > > [1]. https://lore.kernel.org/lkml/20200425114414.GU26573(a)shao2-debi= an/ > > = > > One possibility is that the data-address changes put more stress on the > > TLB, for example, if that region of memory is not covered by a huge > > TLB entry. If this is the case, is there a convenient way to define > > mce_missing_cpus so as to get it out of the way? > = > Yes! I also tried some experiment for dTLB, by adding 3 more cpumask_t > right after 'mce_missing_cpus', so that the total offset will be 4KB. > I expected the regression could be gone, but it turns out to have = > a +2.4% improvement. > = > 16741 -4.5% 15980 +2.4% 17149 = netperf.Throughput_tps > = > Which is still kind of out of our control :) = I bet that the results vary depending on the type of CPU, and also on the kernel address-space layout, which of course also varies based on the Kconfig options. Let's see how the maintainers would like to proceed. Thanx, Paul --===============0916882215342503839==--